In melt spinning at high pull-off speeds, cooling of the filament represents the critical step of the method. The problem lies therein that, on the one hand, the yarn temperature must be lowered drastically and, on the other, the yarn speed must be increased.
Yarn suction nozzles for cooling yarns in melt spinning with speeds of more than 5,000 m/min are known. On the one hand, they take in the yarns and, on the other, serve to supply a cooling gas parallel to the yarns.
Pursuant to the EP-B-0 056 963, such a nozzle is used in conjunction with a heating chamber, the heating chamber being mounted directly underneath the spinning block.
The EP-A-0 244 217 discloses the use of such a nozzle for the same purpose in conjunction with a Venturi nozzle, which is operated with a hot gas. The Venturi nozzle is also mounted directly under the spinning block.
The heating chamber as well as the Venturi nozzle that is operated with a hot gas, both of which are mounted directly below the spinning block, serve to improve the course of the spinning and the yarn properties. As far as the yarn properties are concerned, above all the dyeability is affected positively by these.
The yarn suction nozzle for cooling the yarn is between 50 and 600 mm below the heating chamber in the case of the heating chamber and a sufficient distance below the Venturi nozzle in the case of the Venturi nozzle, so that the air emerging there does not adversely affect the operation the Venturi nozzle. The yarns enter the yarn suction nozzle as an open bundle. Because of the delayed cooling of the yarns, the latter are still quite fluid, that is, solidified only a little, on their way to the yarn suction nozzle.
In this section, the yarns are not stabilized in any way against lateral migrations, that is, against migrations perpendicular to the running direction of the yarns. Such lateral migrations lead to sinusoidal titer fluctuations along the fiber bundle so produced. These fluctuations, in turn, have a negative effect on the dyeability and the strength.